Respiratory Physiology - Respiration under stress and at the limit Flashcards
Respiratory response to exercise
VO2 increases in linear relationship as work rate increases, until reach VO2 max where it plateaus
Ventilation also increases linearly until reach anaerobic threshold, where lactate increases and ventilation increases even more as chemoreceptors are stimulated
Additional physiological changes with exercise
Pulmonary artery, venous and capillary pressures rise
Recruitment and distention of capillaries
Pulmonary vascular resistance falls
Pulmonary diffusing capacity rises
Shifts of O2 dissociation curve
Systemic vascular resistance falls
Effect on barometric pressure and inspired PO2 with increasing altitude
Barometric pressure decreases with altitude
Inspired PO2 therefore also decreases
Effect of altitude on ventilation
Ventilation increases - demonstrated with alveolar gas equation
Acclimatisation to high altitude
pH of CSF and blood normalises over time by bicarbonate buffering
Polycythaemia
Shift of O2 dissociation curve
Increased capillary concentration in muscle
Capillary pressures in high altitude
Uneven hypoxic pulmonary vasoconstriction
Therefore some capillaries exposed to high pressures
Leads to pulmonary oedema
Reverse it by descending from altitude
The bends aka decompression sickness
Nitrogen dissolves into tissue (esp fat tissue) as dive deeper
As come back up, nitrogen comes out of tissue and creates bubbles
Bubbles cause pain in joint + disrupt blood flow + CNS disruption
Management of decompression sickness
Prevention:
- Slow ascent
- Helium mixed gases
Treatment:
- Hyperbaric chamber
Use of Helium mixed gases
Helium has lower density so reduced airway resistance
He less soluble than Nitrogen
Concentration of dissolved O2 in blood with hyperbaric therapy
Maintains oxygenation where these is low oxygen carrying capacity of blood - eg carbon monoxide poisoning
Physiological changes in space
Increased pulmonary capillary volume
Increased pulmonary diffusing capacity
Increased CO and SV
More uniform distribution of lung blood flow and ventilation
Residual volume reduced
Changes in the deposition of aerosol particles (less sedimentation)
Why does pulmonary capillary volume increase in space
No gravitational pooling of blood
Cause for more uniform distribution of lung blood flow and ventilation in space
No gravitational pooling of blood to lower lung zones or compression of lung parenchyma
Pulmonary function in microgravity (space)
O2 uptake and CO2 output unchanged
Alveolar PO2 and PCO2 unchanged
No significant impairment in lung function - resolve when return
Pressure rise rate with diving
Every 10m of descent, pressure increases by 1 atmosphere
